Electronic cards such as telecommunications repeaters and other electronic equipment are often housed in enclosures that are required to bear the elements above ground or below ground. The elements include but are not limited to ground water, sun, rain, salt fog, pollution, heat, cold, as well as fire. Often the underground installations are subjected to partial or total submersion in water and are required to be sealed against a pressure differential. These sealed enclosures are also required to remove energy, usually in the form of heat, generated by the electronic equipment in the enclosures. Many enclosures trap heat generated by the electronics. The build up of heat within these enclosures can cause significant problems for the electronic equipment by challenging the temperature limits of the electronic devices and causing device failure.
The enclosures are designed in a variety of configurations. One design for an electronics enclosure is substantially cylindrical. In some instances, electronics cards mounted within the cylindrical enclosure are oriented tangential to the outer wall. In some designs the cards are mounted such that two cards are stacked together, having an outer card in indirect thermal contact with the enclosure and an inner card parallel to the outer card that may be thermally connected to the outer card.
Many problems have arisen with respect to heat build up within these enclosures. The inner cards run hotter than the outer cards and as a result failure rates are higher for the inner cards. The path from the inner cards to the exterior of the enclosure is significantly longer than the outer cards. Good heat dissipation requires consistent and preferably direct contact between transfer materials e.g. the electronics card, card cages, and housing.
In some designs a card cage is used to contain the electronics cards. Often enclosures include card cages that collect and release heat into the enclosure environment and the heat becomes trapped. These card cages are typically single structures that continually exchange heat between the cards and the air within the enclosures without substantially moving the heat to the exterior of the enclosure. Because the card cage is one structure the structure becomes saturated with energy and can increase the heat build up within the enclosure.
Some applications provide a series of materials through which heat is transferred from the electronics devices to the ambient air. For example some electronic enclosures transfer heat from multiple electronic cards to a single card cage to a conductive liner to one or more heat sinks to an enclosure.
It is difficult to get and keep the electronics cards in contact with the card cage. If good contact is not maintained poor heat dissipation results and the rate of failure for the electronic devices is high. Some enclosures include active devices such as cams that require a technician or user to engage the device. The active devices force the electronic cards and card cage into contact but are prone to failure and are often overlooked by technicians and not engaged. Additionally, electronic cards come in many different styles and contact with heat transfer members do not take into consideration open frame repeaters where the repeaters are encased in a box or frame with a portion of the sides removed.
Electronics cards are also susceptible to vibration and gravity. Cards are often retained in an enclosure only by an electrical connection such as insertion into an electrical socket. Due to vibration during shipping and operation the cards can become loose and dislodged from the electrical connectors. The cards can also be loosened when subjected to mounting locations that force the electronic cards to “hang” from the electrical socket. The use of active retention devices, such as cams, requires human intervention and is not reliable. Loose connections cause operation errors and result in time consuming and costly service calls.
Often connector blocks are supposed to receive an electronics card in a specific orientation and problems arise when the card is able to be plugged into the connector block in reverse.
Electronic equipment enclosures such as repeater housings are often heavy and cumbersome. The enclosures are difficult to carry and maneuver in small places such as mounting on telephone poles or into manhole compartments. Any enclosure which exceeds a set weight is required to be equipped with a lifting mechanism for attaching hoisting cables or chains. Often enclosures are lifted using cable with bundled wires that has been potted into the bottom of the enclosure. The stress caused by the weight of the enclosure can lead to pull out of the potted cable.
In addition, enclosures are subjected to costly replacement when the heat sinks or other exterior components are deteriorated by corrosion or otherwise damaged. Complete replacement is costly and time consuming often causing a drop in service for subscribers. In particular, when assembled welding locations are susceptible to faster corrosion rates.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved enclosure for electronics equipment that overcomes the above noted imitations.